Evolution Of Atmospheric Water Cycle Under The Sea-Ice Rapid Change In Arctic

Based on the monthly and daily ERA-Interim reanalysis data from 1979 to 2016,the atmospheric water cycle over the Arctic Ocean was studied by various statistical diagnostic methods.The spatial and temporal variations of water vapor,local precipitation,evaporation,and the meridional atmospheric moisture transport were analyzed in detail.By using the six Great Arctic Rivers discharge data from 1965 to 2016,the seasonal and interannual variations of river discharge were investigated as well,We further defined the Arctic Discharge Concentration Degree(DCD)and Concentration Period(DCP)index to quantify characteristics of the annual distribution of river discharge.Meanwhile,we discussed the factors affecting the change of local river discharge by analyzing the process of the surface water cycle in the land.In addition,the spatial and temporal variability of the correlation between sea ice area and atmospheric water vapor was studied by using the sea ice observation data from the National Snow and Ice Data Center(NSIDC).Finally,we analyzed the sea ice-atmosphere interactions in key regions of the Arctic under two scenarios in which the global mean temperature increases by 1.5? and 2.0? relative to pre-industrial levels using the CESM.The conclusions are as follows:In the past 38 years,the atmospheric water vapor of the Arctic has increased significantly,the trend accelerated after the mid-1990s and the increase in summer and autumn is greater than that in winter and spring.The humidity inversions can be found in most of the Arctic in winter,however,they are limited to the Marginal sea zone in summer.Also,they are the thickest in winter but the strongest in summer.The seasonal variation of precipitation in the Arctic Ocean has significant spatial differences.In the North Atlantic,the precipitation in summer is more than winter,but the Central Arctic Ocean is the opposite.In recent years,the snowfall and rainfall in the central Arctic Ocean have both increased significantly.But in the Atlantic sector,the rainfall has increased and snowfall has decreased.Also,the number of rainy days has increased and snowfall days has decreased,which imply the precipitation over Arctic Ocean is conversing from solid to liquid.Further analysis indicates the increase of precipitation in the Kara Sea and Chukchi Sea is mainly due to the enhancement of local evaporation,while the Barents Sea,the Eastern Siberian Sea and the Laptev Sea are subject to local evaporation and moisture convergence flux.In the past 52 years,the Arctic river discharge has shown an increasing trend.The growth rate of the Eurasian side(2.16%decade-1)is higher than that of North America(1.50%decade-,).Meanwhile,the discharge of six major rivers generally increases in May(the month of melting)but decreases in summer,which is especially obvious in the Yenisey River.Further analysis shows that the annual distribution pattern of the six major rivers discharge is getting more dispersed during the years.Based on the process of water budget in the Arctic basin,we reveal that the positive correlation between the total net precipitation in the basin from May to next April and the accumulated river discharge from August to next July is the greatest.By using multiple stepwise regression analysis,we further point out that the temperature is the dominant factor affecting the interannual variation of discharge in May while the moisture convergence flux in the previous has the greatest impact on summer discharge.There are significant negative correlations between the Arctic sea ice area and the upper water vapor in the same period.In the cold season(November-May),the strongest negative correlation located in the Barents-Kara sea of Arctic Atlantic Sector,while in the warm season(June-October),it is mainly in the Pacific Sector.The positive anomaly of water vapor and its positive feedback to temperature and surface downward longwave radiation can trigger the initial melting of sea ice,which can also continue to affect the subsequent melting process of sea ice.Under the scenario of global warming of 1.5 C and 2.0 C,the atmospheric water vapor in Arctic would increase significantly and Arctic sea ice would decrease dramatically.In summer,the central Arctic sea ice area is negatively correlated with water vapor within two months ahead and behind,and the correlation is greatest in the initial warming stage and weakens significantly after the temperature stabilizes.In winter,the Barents Sea ice area is negatively correlated with water vapor in the same period and lagging for two months,and the negative correlation is more significant at 2.0?.